Sparkle Power’s 250W ATX12V 80 Plus SPI250EP

Sparkle Power’s 250W 80 Plus SPI250EP seems a throwback to yesteryear. Is there any place in today’s PC world for such a modest ATX12V power supply? Oh, most definitely.

March 21, 2008 by Mike
Chin

The SPI250EP appears at first glance to be a throwback to computer technology nearly a decade ago. What’s a measly 250W-rated, generic-looking ATX12V power supply doing in a website for PC enthusiasts in 2008? Look more closely and you’ll see the number "80" that’s part of the 80 Plus logo, which identifies the product as a modern power supply >80% efficient at all loads from 20% of rated power all the way to full power.

250W rating and 80 Plus
tag make this ATX12V PSU unusual for 2008.

Most SPCR readers know about 80 Plus. In fact, an article about 80 Plus was posted on the front page just days ago. There are hundreds of 80 Plus approved, high efficiency power supplies. What makes this one special?

The vast majority of 80 Plus approved PSUs are rated for 300W or higher, the mean being somewhere over the 400W mark. This is significant if you’re trying to achieve the lowest power consumption with very low power computer components: You’re most concerned about the efficiency at 20% load.

A 400W 80 Plus power supply is assured to reach 80% efficiency from 80W (which is 20% of 400W) on up. What if your system only draws 30W? Chances are, that 400W PSU will do no better than perhaps 50~60% efficiency at this low output.

The efficiency vs power load plot of any PSU is a bell curve, similar to the efficiency curve of most machines. The highest efficiency is found typically at 50~75% of rated power. At maximum power, rising temperature makes efficiency sag, and as the load is reduced, the efficiency sags because the components and circuits are optimized for higher loads.

A 250W 80 Plus power supply is assured to have >80% efficiency down to 50W, compared 80W for a 400W model. This is the crux of our interest in the SPI250EP: It is the lowest rated ATX12V PSU on the 80 Plus approved list. We can hope that its efficiency doesn’t fall off too fast below 50W.

Note expanded and limited vertical scale. The graph shows the relative efficiency difference at lower power for two PSUs that achieve the same maximum efficiency.

Are there many systems today that have <50W power demand?

There is a surprising high number of commercially available PCs that qualify as "Category A" desktops under the Energy Star Computer Specification v.4. There are 127 Category A models, defined as PCs that idle at 50W AC or lower, on Energy Star’s Computers Product List – Desktops & Integrated Computers dated Feb 28, 2008. Based on what we know about a computer’s power consumption patterns, when pushed to full load under real applications, most of these machines will demand no more than about 2.5X the idle power, which means ~125W peak. Apply the typical AC/DC conversion loss, and we’re probably looking at peak power demand of perhaps 100W in DC.

For the do-it-yourselfer, the number of component options for assembling low power systems is not small, and it’s growing. Very low power CPUs that idle at just a few watts and max out at under 30W are available from from AMD, Intel and VIA. Motherboards with excellent integrated graphics for 2D work are both inexpensive and energy efficient. Even 3D performance is not bad with the latest chipsets such as the AMD 780G. A 2.5" mobile SATA hard drive of >300GB capacity that draws no more than a watt or two can easily take the place of the 7~12W 3.5" desktop drive. Basically, these are the same components used in some of the very low power Energy Star Category A commercial systems. The single biggest power bottleneck in such systems is usually the power supply, where upwards of 50% of incoming AC power can be lost, due low efficiency at such low output loads.

The unusual picoPSU with a high efficiency AC/DC power adapter has been the power supply of choice among ultra low power, silent system builders, as it can maintain nearly 80% efficiency even down to 20W loads. But it’s not cheap and it has limitations, the biggest one being the difficulty of sourcing good AC/12VDC adapters rated for more than ~120W (if you want any headroom).

We recently identified and reviewed another Sparkle, the 80 Plus approved 220W SPI220LE, as a possible option for a high efficiency low power PSU. While not quite the equal of the picoPSU, it achieved 73% efficiency down to 20W and 78% at 30W, but its Flex ATX form factor makes it difficult for most DIYers to use.

So what are the main facts about this 250W PSU?

A couple of notes:

• Stating that there are two 12V lines on a PSU that cannot deliver 18A total into 12V is just silly. The EN safety regulation this was meant to satisfy only calls for current to be limited to <240VA.
• The +3.3V and +5V line current capacity seems a bit high for an ATX12V PSU rated so low.
• The target market for the SPI250EP is not a DIY retail end user, but a commercial system integrator.

EXTERNAL TOUR

The SPI250EP is a basic straight-through forced airflow design with an 80mm fan. The generic-gray casing looks identical to that used in Zalman and Nexus PSUs made by SPI (and/or its affiliate Fortron Source Power) some years ago when they were just about the only quiet PSU options around. The absence of a VAC selector switch is due to the auto-input voltage feature; the absence of a power switch is about saving pennies. The stamped grill is actually quite open, probably very similar in aerodynamic aspects to the more attractive circular wire grill.

No switches on back panel.

The intake end of the PSU is nicely open and unrestricted to airflow. There would be no point making this vent any larger than it is.

The intake end is nicely unrestricted for airflow.

The label.

CABLES AND CONNECTORS

There are five cable sets, all of which are very short. The PSU is meant to go into a small, modest system.

• 12″ cable for main 20+4-pin ATX connector
• 9″ cable for 4-pin AUX12V connector
• 1 x 13″ cable with one 4-pin IDE drive connectors
• 1 x 18″ cable with two 4-pin IDE drive connectors and one
  floppy connector
• 1 x 20″ cables with two SATA drive connectors

All the cables are short.

INTERIOR

The overall build looks fine, reminiscent, again, of lower powered PSUs from yesteryear. The PCB is laid out reasonably neatly, the components appear to be of average quality, and the heatsinks are small, but probably as big as they need to be. The fan leads are soldered to a small PCB mounted on a heatsink.

Three transformers in the center.

Open space behind fan suggests low turbulence.

Dual 470uF capacitors, heatsink fin detail and transformers.

View from intake side.

Peripheral PCBs.

The 80x25mm ball-bearing fan is made by Yate Loon, and it is rated for 12V, 0.1A. It’s a slow speed model, rated for 2100 RPM at 28 dBA.

TESTING

For a fuller understanding of ATX power supplies, please read
the reference article Power
Supply Fundamentals & Recommended Units.
Those who seek source materials can find Intel’s various PSU design
guides at Form Factors.

For a complete rundown of testing equipment and procedures,
please refer to SPCR’s PSU Test Platform V.4.
The testing system is a close simulation of a moderate airflow
mid-tower PC optimized for low noise.

In the test rig, the ambient temperature of the PSU varies
proportionately with its output load, which is exactly the way it is in
a real PC environment. But there is the added benefit of a high power
load tester which allows incremental load testing all the way to full
power for any non-industrial PC power supply. Both fan noise and
voltage are measured at various standard loads. It is, in general, a
very demanding test, as the operating ambient temperature of the PSU
often reaches >40°C at full power. This is
impossible to achieve with an open test bench setup.

The 120mm fan responsible for “case airflow” is deliberately
run at a steady low level (6~7V) when the system is run at lowloads. When the test loads become greater, the 120mm fan is turned up
to a higher speed, but one that doesn’t affect the noise level of the
overall system. Anyone who is running a system that draws 400W or more
would definitely want more than 20CFM of airflow through their case,
and at this point, the noise level of the exhaust fan is typically not
the greatest concern.

Great effort has been made to devise as realistic
an operating environment for the PSU as possible, but the thermal and
noise results obtained here still cannot be considered absolute. There
are too many variables in PCs and too many possible combinations of
components for any single test environment to provide infallible
results. And there is always the bugaboo of sample variance. These
results are akin to a resume, a few detailed photographs, and some
short sound bites of someone you’ve never met. You’ll probably get a
pretty good overall representation, but it is not quite the same as an
extended meeting in person.

SPCR’s
high fidelity sound recording system was used to
create MP3 sound files of this PSU. As with the setup for recording
fans, the position of the mic was 3″ from the exhaust vent at a 45°
angle, outside the airflow turbulence area. The photo below shows the
setup (a different PSU is being recorded). All other noise sources in
the room were turned off while making the sound recordings.

INTERPRETING TEMPERATURE DATA

It important to keep in mind that fan speed varies with temperature,
not output load. A power supply generates more heat as output
increases, but is not the only the only factor that affects fan speed.
Ambient temperature and case airflow have almost as much effect. Our
test rig represents a challenging thermal situation for a power supply:
A large portion of the heat generated inside the case must be exhausted
through the power supply, which causes a corresponding increase in fan
speed.

When examining thermal data, the most important indicator of
cooling efficiency is the difference
between intake and exhaust. Because the heat generated in the PSU
loader by the output of the PSU is always the same for a given power
level, the intake temperature should be roughly the same between
different tests. The only external variable is the ambient room
temperature. The temperature of the exhaust air from the PSU is
affected by several factors:

• Intake temperature (determined by ambient temperature and
  power output level)
• Efficiency of the PSU (how much heat it generates while
  producing the required output)
• The effectiveness of the PSU’s cooling system, which is
  comprised of:
  • Overall mechanical and airflow design
  • Size, shape and overall surface area of heatsinks
  • Fan(s) and fan speed control circuit

The thermal rise in the
power supply is really the only indicator we have about all of the
above. This is why the intake temperature is important: It represents
the ambient temperature around the power supply itself. Subtracting the
intake temperature from the exhaust temperature gives a reasonable
gauge of the effectiveness of the power supply’s cooling system. This
is the only temperature number that is comparable between different
reviews, as it is unaffected by the ambient temperature.

TEST RESULTS

Ambient conditions during testing were 21°C and 19 dBA. AC
input was 120V, 60Hz.

ANALYSIS

1. EFFICIENCY — This is a measure of AC-to-DC conversion efficiency. The ATX12V Power Supply Design Guide recommends 80% efficiency or better at all output power loads. 80% efficiency means that to deliver 80W DC output, a PSU draws 100W AC input, and 20W is lost as heat within the PSU. Higher efficiency is preferred for reduced energy consumption and cooler operation. The latter allows reduced cooling airflow, which translates to lower noise.

Above ~50W, the efficiency of the SPI250EP exceeded 80% all the way to full output. Below 50W, efficiency dropped to 78% by 40W, and to 67% by 20W. The SPI250EP is not quite the equal of its FlexATX 220W brethren.

We began testing at 20W load quite recently, so there are only a handful of PSU samples for this data point. All the tested data is compiled in the table below, ordered by efficiency at 20W. This is simply a point of comparison. Keep in mind that the 20W efficiency measurements are subject to greater error than the ones at higher power because the actual measured numbers are that much smaller (i.e., at 20W, 1W = 5%, while at 40W, 1W = 2.5%).

Low Load Efficiency Comparison
PSU	20W	30W	40W	65W	90W
picoPSU, 80W brick	79.4%	n/a	83.6%	84.8%	84.7%
picoPSU, 120W brick	77.7%	n/a	85.6%	87.1%	87.1%
Sparkle SPI220LE	73.0%	77.7%	80.5%	82.8%	83.8%
Seasonic EcoPower 300	68.0%	73.8%	75.4%	81.1%	82.4%
Sparkle SPI250EP	67.2%	76.0%	78.3%	81.5%	83.4%
Seasonic M12II-430	66.2%	n/a	74.9%	78.6%	81.4%
Enermax Modu82+ 625W	66.1%	n/a	78.4%	80.0%	80.9%
Seasonic S12II-380	65.4%	n/a	76.3%	79.4%	81.5%
Corsair TX650W	62.9%	n/a	70.9%	77.5%	81.9%
Corsair VX450W	61.3%	n/a	72.8%	79.1%	80.1%
NOTE: The highest efficiency reached is not indicated by the 90W column; many models don’t reach peak efficiency till > 50% of rated power.

The low power efficiency is not quite the equal of the earlier tested SPI220LE, but at 30W and higher, it gets within 1~2%. Surprisingly, the 625W Enermax Modu82+ matches its efficiency at 40W. This throws the whole argument for lower rated PSUs into question: What’s the point if a 625W PSU can match the efficiency of a 250W PSU at a load as low as 40W? Doesn’t the efficiency curve apply? The answer to these questions is in the name of the Enermax. Modu82+ refers to the "Bronze" category of 80 Plus that this product is supposed to fall into: It has 82% efficiency at 20% load, not just 80% efficiency. Ergo, if we had a "Bronze" 80 Plus 250W PSU, it would have higher efficiency at 40W than the Modu82+ 625.

However, it’s important to note that at 20W load, even a big 10% efficiency difference accounts for only 2W. The 78.4% efficiency of the Sparkle SPI250EP at 40W load compared to the Corsair TX650W’s 70.9% is a real difference of 5W.

2. VOLTAGE REGULATION refers to how stable the output voltages are under various load conditions. The ATX12V Power Supply Design Guide calls for the +12, +5V and +3.3V lines to be maintain within ±5%. VR in the SPI250EP sample was excellent. There was no significant sag on any of the lines, especially the all-important 12V line, even up to the rated output.

3. AC RIPPLE refers to unwanted "noise" artifacts in the DC output of a switching power supply. It’s usually very high in frequency (in the order of kilohertz or megahertz). The peak-to-peak value is measured. The ATX12V Guide allows up to 120mV (peak-to-peak) of AC ripple on the +12V line and 50mV on the +5V and +3.3V lines. Ripple in the SPI250EP stayed well within the 1% allowed by ATX12V on all voltage lines at all loads.

4. POWER FACTOR is ideal when it measures 1.0. In the most practical sense, PF is a measure of how "difficult" it is for the electric utility to deliver the AC power into your power supply. High PF reduces the AC current draw, which reduces stress on the electric wiring in your home (and elsewhere up the line). It also means you can do with smaller, cheaper UPS backup; they are priced according to their VA (volt-ampere) rating. PF on this sample was close to perfect across all loads, as is the norm
for most power supplies with active PF correction circuitry.

5. AC INPUT VOLTAGE TESTS

Low VAC: This is to check the stability of the PSU under brownout conditions where the AC line voltage drops from the 110~120V norm. The unit was pushed down to 100VAC without any problems. DC output voltage regulation remained unchanged from that achieved at 120VAC.

LOW VAC TEST: Sparkle SPI250EP @ 200W load
VAC	AC Power Input	Efficiency
242	234W	85.5%
120	241W	82.9%
110	242W	82.6%
100	244W	82.0%

240 VAC Input: Most power supplies achieve higher efficiency with higher AC input voltage. SPCR’s lab is equipped with a 240VAC line, used to check power supply efficiency for the benefit of those who live in 240VAC mains regions. The 240VAC efficiency advantage measured 2.6 percentage points higher at 200W load.

6. LOW LOAD TESTING revealed no problems starting at low loads. The power draw at standby was a super low 0.3W, and power
consumption with no load was very good at 6.5W.

7. TEMPERATURE & COOLING

Cooling was excellent, with the temperature rise through the PSU staying in single digits even at full load. Given the high efficiency and modest output power, this result is not a surprise. It’s far superior to the FlexATX SPI220LE, which is hampered by a tiny fan, high component density (airflow impedance) and small form factor.

8. FAN, FAN CONTROLLER and NOISE

The acoustics are surprisingly good. The noise at turn-on is low enough that the quality of the sound isn’t much of a factor. It’s somewhat tonal but at 19 [email protected], it’s a very low level that’s probably inaudible in most environments. The noise of the PC it’s in or the room ambient itself would probably swamp it. From up close, you can hear both fan and electronic noise, the latter a bit higher in level than other PSUs tested recently. The electronic noise is a bit of high frequency squealing that never quite disappears until the fan speeds up considerably at higher loads, when the turbulence noise covers it up. It might be bothersome if you have very sensitive hearing, very quiet components and a super low ambient.

The classic ball-bearing fan clicking / buzzing is mostly absent here; hopefully, this is not just a case of a lucky sample. Even at full load, with the feed voltage just uner 12V, the measured SPL was only 28 [email protected]. which is the actual specification of the fan by itself. In all these years of PSU testing, this is the first time that the measured SPL of a PSU has not been many decibels higher than the stated SPL for its fan.

The fan controller appears to have a linear temperature-to-voltage curve, as with most SPI and FSP power supplies reviewed in the past. That is, any temperature increase causes a corresponding proportionate increase in fan voltage. But because the power output is so modest and the efficiency high, the PSU remains pretty quiet till over 150W load.

The fan controller is somewhat sensitive, with sudden changes in load causing fairly quick changes up or
down in fan speed. This effect is not that audible, however, and certainly much better than the earlier SPI220LE.

The high starting voltage of 6.2V to the fan is quite useful for the modder considering a fan swap. Most 12VDC 80x25mm fans will start easily with that voltage. A swap for a smoother, quieter fan in combination with a fresh air intake duct (or a case with a dedicated PSU chamber such as the Antec P180-182-190, Fusion, NSK3480 or Mini P180 — though cables are too short for these cases) would make the SPI250EP a "silent" power supply. Basically any 80mm 12VDC fan rated close to 0.1A would work; the point would be to use one smoother and quieter than the stock fan.

MP3 SOUND RECORDINGS

Each of these recording start with 6~10 seconds of the ambient sound of the room, followed by 10 seconds of
the product’s noise.

• Sparkle Power SPI250EP at 40W output, 19
  [email protected]: One
  meter, One
  foot (30cm)
• Sparkle Power SPI250EP at 150W output, 22
  [email protected]: One
  meter
• Sparkle Power SPI250EP at 250W output, 28
  [email protected]: One
  meter

Sound Recordings of PSU
Comparatives

• Sparkle Power SPI220LE at 90W
  output, 24 [email protected]: One
  meter
• Corsair VX450W at up to ~250W output, 22 [email protected]: One
  meter, One
  foot (30cm)
• Enermax Modu82+ 625W at 20~150W output, 19 [email protected]: One meter recording, One foot recording
• Enermax Modu82+ 625W at 300W output, 22 [email protected]: One meter
• Seasonic S12II-380 at up to ~200W output, 21 [email protected]: One
  meter

CONCLUSIONS

The Sparkle Power SPI250EP is the lowest capacity 80 Plus approved ATX form factor power supply we’ve tested thus far. Our sample meets the 80 Plus requirements, and it is 80% efficient even down to a low 50W load, which is better than most other PSUs.

Parameters such as voltage regulation, power factor, ripple and low load performance were all fine. The SPI250EP is a more convenient and probably lower-cost all-in-one alternative to the more complex, multi-part picoPSU for energy efficiency. It’s not quite as efficient, but the convenience and far greater power headroom may make up for the few watts difference.

The acoustics are very good, good enough for this modest Sparkle to be considered an excellent, no-fuss, solution for a quiet, low power system. With a little bit of work, an experienced system builder could easily create a silent PC incorporating the SPI250EP. For the green-and-silent PC system builder, this is a very useful product. The biggest challenge for DIY computer enthusiasts may be to find a store that sells it.

Much thanks to Sparkle Power International for this review sample.

* * *

SPCR Articles of Related
Interest:
Power Supply Fundamentals
Recommended
Power Supplies

Power
Distribution within Six PCs
SPCR
PSU Test Rig V.4
picoPSU
EnermaxModu82+ 625
Corsair VX450W
Seasonic SS-300SFD 80 Plus: Little Big PSU

* * *

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